FIG. 1 illustrates a track-type tractor 100 employing a pair of endless track assemblies 102 (one shown) of this invention thereon. Although the track assembly is particularly adapted for use on a tractor, it should be understood that the track assembly will find application to other vehicles, such as track-type excavators or any other type of off-road vehicle or machinery. In the tractor application illustrated in FIG. 1, each track assembly 102 is mounted in a conventional manner on a drive sprocket 104, an idler 106, a plurality of longitudinally spaced track rollers 108, and a pair of upper guide or carrier rollers 110, when needed.
Referring to FIGS. 2 and 3, a track assembly 102 comprises a plurality of track shoes 112 which are pivotally interconnected by an articulated link assembly 114. Link assembly 114 is disposed intermediate the widths of track shoes 112 and includes a plurality of pairs of links 116, pivotally interconnected together by standard pin and bushing assemblies 118. The teeth 120 of drive sprocket 104 engage the bushings of pin and bushing assemblies 118 to drive track assembly 102 in a conventional manner with the track assemblies being guided by idler 106 and rollers 108 and 110 which engage upper rail portions of links 116. The main difference between the configurations of the track assembly of FIGS. 2 and 3 is that FIG. 2 is an inline configuration, so called as the drive sprocket is in-line with the front idler wheel forming a substantially ovular path for the track, while FIG. 3 shows an elevated configuration, so called as the drive sprocket is vertically above the lower idler wheels forming a substantially triangular path for the track.
With continued reference to FIGS. 2 and 3, the lower rollers are often called track rollers 108 as they support the weight of the vehicle and transfer it to the track and then to the ground while the upper rollers are often called carrier rollers 110 as they only carry or support the track, limiting or sometimes modifying the catenary hang of the track. The drive sprockets 104 have segments 122 with drive teeth 122 connected to them or integrally formed therewith that mesh with the links 116 in the track assembly 102, powering movement of the track, and thus the vehicle. The shoes 112 include provide movable platforms that engage the ground and include ribs or grousers 124 that penetrate the ground, providing traction. The idler wheels 106 lack teeth but ride between the links 116 (see G in FIG. 5) and on top of the rails (see 130 of FIG. 4) of the links 116, limiting side to side movement of the track. Similarly, the rollers 108, 110 provide a conduit for the transfer of weight, and in many cases, provide a way to adjust the tension in the track. The rollers 108, 110 also ride between the links 116 and on top of the rails of the links 116, limiting side to side movement of the track.
Turning now to FIGS. 4 and 5, they show an example of a link assembly 114 that includes a pair of track links 116 that are joined together by a track pin and bushing assembly 118 in a manner consistent with the tracks illustrated in FIGS. 2 and 3. The track pin and bushing assembly 118 form a joint that includes a cylindrical pin 126, and a rotatable tubular bushing 128. The pin 126 has opposite end portions 132 (best seen in FIG. 5), each of which is pressed and non-rotatably mounted into a respective one of the bore 134 formed by a protruding boss 136 of the outboard end collars 138 of each link 116 in a link set 114. The pin and bushing assembly 118 further includes a method and device for mechanically interlocking the pin 126 within such bores 134 to prevent any axial movement of the links 116 along a longitudinal or cylindrical axis 140 of the pin 126.
One type of method for mechanically interlocking the pin 14 to the links 16 is that apparatus disclosed and described in U.S. Pat. No. 4,618,190, entitled Track Joint Retaining Apparatus, issued Oct. 21, 1986, and which is incorporated hereinto by this reference. Another preferred mechanically interlocking method comprises a circumferentially disposed, generally arcuately shaped groove formed about each of the end portions of the pin and at least one mechanically formed nodule which protrudes radially inwardly from each of the bores into a respective one of the grooves. The mechanically formed nodules are preferably formed by using a punch device. Preferably, a pair of such punch devices are located perpendicular to the pin axis on each of the flats provided on the pin boss. The application of a sufficient force of the punch devices will result in the extrusion of the boss metal into the groove. This method is disclosed in U.S. Pat. No. 5,183,318, entitled Endless Track Chain for Track-Type Vehicles, issued Feb. 2, 1993, and which is incorporated herein by reference. Other methods for achieving this are also available and may be used.
Referring to FIG. 6, there is shown a portion of an undercarriage for a track-type machine that uses a track assembly 102 and link assembly 114 that are similar to those described thus far herein. The tubular bushing 128 is provided with a pin bore 142 which is of a size sufficient to freely rotatably mount the bushing 128 about the pin 126. Bushing 128 has a pair of opposite end faces 144 and is of a size to extend between and to freely rotatable relative to the inboard end collars 146.
As shown in FIG. 6, each link assembly includes inboard links 116 and outboard links 116′. Inboard links 116 and outboard links 116′ may be coupled together with a plurality of additional inboard and outboard links (not shown), to form an endless chain extending about a conventional drive mechanism including one or more track idlers and a drive sprocket. This may be used in a variety of track-type machines, such as a track-type tractor, tracked excavator, tracked loader, or the like. As will be further apparent from the following description, one practical implementation of the teachings set forth herein is contemplated to be in track-type tractors used in particularly harsh field conditions, such as mines and landfills.
The track pin 126 may be press fit with outboard links 116′. In one embodiment, retention rings 148 or some other mechanism for positive pin retention may be coupled with pin 126 to enhance the strength of the coupling with outboard links 116′. In the embodiment shown, inboard links 116 and outboard links 116′ include S-shaped links, however the present disclosure is not limited in this regard and straight link track might also be used. During operation as already discussed, one or more track idlers and a drive sprocket may engage with the bushing 128 to guide and provide power to the track in a conventional manner. As will be familiar to those skilled in the art, some structure for lubricating surfaces which move against one another within the track assembly may be desirable. To this end, the pin 126 may include an oil passage 150 which serves as an oil reservoir for supplying oil to desired locations within track segment.
During track assembly at the factory or during track repair or servicing, lubricating oil may be supplied into passage 150, and the oil passage may be plugged to seal the lubricating oil therein. A set of seals 152 may also be provided, which fluidly seal between outboard links 116′ and bushing 128 to retain oil within the link assembly 114. The link assembly 114 also includes a set of thrust rings 154, each positioned between the bushing 128 and one of outboard links 116′. Thrust rings 154 can react to thrust loads through the link assembly 114, and may be configured to prevent compressive forces on seals 152 which can otherwise impart a tendency for seals to fail. Each of thrust rings 154 may be uniquely configured to provide a robust mechanism for reacting thrust loads, but also facilitate the transfer into and maintaining of oil within a region of the link assembly 114 defined between bushing 128 and outboard links 116′, and also between each seal 152 and the pin 126. It should be noted that the oil passage is shown in dotted lines, indicating that in certain embodiments, it may not be present, such as will now be described.
FIG. 7 shows another track link assembly 114 that is known in the art that lacks an oil passage or other void that surrounds the longitudinal axis of the pin. This link assembly 114 includes a seal assembly 156 that includes first and second seal members 158, 160 that provide sealing between the inboard end collars 146 of the outboard link 116′ and the bushing 128. Each of the seal assembly 156 is disposed within each of the counterbores 162 between the shoulder 164 of the counterbore and the adjacent outer end face 144 of the bushing 128 and in sealing engagement against the outer end face 144. These type of seals are often referred to as rotating face seals as they allow the bushing to rotate relative to the pin 126 and outboard link while still keeping lubrication from leaking. Also, thrust rings are provided between the pin and seal assembly for reasons already explained above. The pin includes regions that absorb loads from the links either directly or indirectly through the bushing. Specifically, region 166 is in contact with the outboard link 116′ while region 168 is in contact with the bushing 128 directly underneath the inboard link 116.
As can be imagined, the track pin of any of the embodiments discussed herein supports a heavy load during use and any failure of the track pin also results in a failure of the track of the vehicle, causing an undesirable down time for that vehicle. As a result, track pins are usually hardened to improve their durability in the field. However, hardening such track pins can be very costly.
Accordingly, it is desirable to reduce the cost of track pin manufacture without compromising the durability of the track pin in the field.